1. Go to "Start" -> "Run".
2. Write "CMD" and press on "Enter" key.
3. Write the command "
net statistics server" and press on "Enter" key.
4. The line that start with "Statistics since …" provides the time that the server was up from.
The command "
net stats srv" can be use instead.
Taken from:
http://support.microsoft.com/kb/555737
Other possibility: the command
systeminfo
And another:
net statistics workstation.